Reagent concentration, temperature, and residence time are known factors that drive chemical reactions. Combustion chemical vapor deposition (combustion CVD) processes are no different. The significance of these factors and their controlling process parameters has been well documented.
Combustion chemical vapor deposition (combustion CVD) is a relatively new technique for the growth-of coatings. Combustion CVD is described, for example, in U.S. Pat. Nos. 5,652,021; 5,858,465; and 6,013,318, each of which is hereby incorporated herein by reference in its entirety.
Conventionally, in combustion CVD, precursors are dissolved in a flammable solvent and the solution is delivered to the burner where it is ignited to give a flame. Such precursors may be vapor or liquid and fed to a self-sustaining flame or used as the fuel source. It will be appreciated that when used with a self-sustaining flame, a solvent may or may not be required. A substrate is then passed under the flame to deposit a coating.
There are several advantages of combustion CVD over traditional pyrolytic deposition techniques (such as CVD, spray and sol-gel, etc.). One advantage is that the energy required for the deposition is provided by the flame. A benefit of this feature is that the substrate typically does not need to be heated to temperatures required to activate the conversion of the precursor to the deposited material (e.g., a metal oxide). Because the energy needed for deposition is provided by the flame, the need for additional energy sources may be reduced and the technique may be amendable to temperature-sensitive substrates. Also, a curing step (typically required for spray and sol-gel techniques) typically is not required. Another advantage is that combustion CVD techniques do not necessarily require volatile precursors. If a solution of the precursor can be atomized/nebulized sufficiently (e.g., to produce droplets and/or particles of sufficiently small size), the atomized solution will behave essentially as a gas and can be transferred to the flame without requiring an appreciable vapor pressure from the precursor of interest. Still another advantage relates to the ability to operate combustion CVD apparatuses at atmospheric conditions, thereby reducing equipment costs compared to techniques that require a controlled environment.
Conventional combustion CVD processes involve passing a precursor material directly through the entire length of the flame by inserting it into the combustion gas stream prior to being combusted. In some conventional techniques, a precursor/solvent solution is used as the fuel source. The temperature and residence time profile experienced by the precursor is controlled by the combustion conditions and/or burner-to-substrate distance.
It will be appreciated that combustion deposition techniques may be used to deposit metal oxide coatings (e.g., single-layer anti-reflective coatings) on glass substrates, for example, to alter the optical properties of the glass substrates (e.g., to increase visible transmission). To this end, conventional combustion deposition techniques were used by the inventor of the instant application to deposit a single layer anti-reflective (AR) film of silicon oxide (e.g., SiO2 or other suitable stoichiometry). The attempt sought to achieve an increase in light transmission in the visible spectrum (e.g., wavelengths of from about 400-700 nm) over clear float glass with an application of the film on one or both sides. The clear float glass used in connection with the description herein is a low-iron glass known as “Extra Clear,” which has a visible transmission typically in the range of 90.3% to about 91.0%. Of course, the examples described herein are not limited to this particular type of glass, or any glass with this particular visible transmission.
The combustion deposition development work was performed using a conventional linear burner with 465 holes even distributed in 3 rows over an area of 0.5 cm by 31 cm (155 holes per row). By way of example and without limitation, FIG. 1a shows a typical linear burner, and FIG. 1b is an enlarged view of the holes in the typical linear burner of FIG. 1a. As is conventional, the linear burner was fueled by a premixed combustion gas comprising propane and air. It is, of course, possible to use other combustion gases such as, for example, natural gas, butane, etc. The standard operating window for the linear burner involves air flow rates of between about 150 and 300 standard liters per minute (SLM), using air-to-propane ratios of about 15 to 25. Successful coatings require controlling the burner-to-lite distance to between about 5-50 mm when a linear burner is used.
Typical process conditions for successful films used a burner air flow of about 225 SLM, an air-to-propane ratio of about 19, four passes of the substrate across the burner, a burner-to-lite distance of 35 mm, and a glass substrate velocity of about 50 mm/sec.
FIG. 2 is a simplified view of an apparatus 200 including a linear burner used to carry out combustion deposition. A combustion gas 202 (e.g., a propane air combustion gas) is fed into the apparatus 200, as is a suitable precursor 204 (e.g., via insertion mechanism 206, examples of which are discussed in greater detail below). Precursor nebulization (208) and at least partial precursor evaporation (210) occur within the apparatus 200. The precursor could also have been delivered as a vapor reducing or even eliminating the need for nebulization The flame 18 may be thought of as including multiple areas. Such areas correspond to chemical reaction area 212 (e.g., where reduction, oxidation, and/or the like may occur), nucleation area 214, coagulation area 216, and agglomeration area 218. Of course, it will be appreciated that such example areas are not discrete and that one or more of the above processes may begin, continue, and/or end throughout one or more of the other areas.
Particulate matter begins forming within the flame 18 and moves downward towards the surface 26 of the substrate 22 to be coated, resulting in film growth 220. As will be appreciated from FIG. 2, the combusted material comprises non-vaporized material (e.g., particulate matter), which is also at least partially in particulate form when coming into contact with the substrate 22. To deposit the coating, the substrate 22 may be moved (e.g., in the direction of the velocity vector). Of course, it will be appreciated that the present invention is not limited to any particular velocity vector, and that other example embodiments may involve the use of multiple apparatuses 200 for coating different portions of the substrate 22, may involve moving a single apparatus 200 while keeping the substrate in a fixed position, etc. The flame 18 is about 5-50 mm from the surface 26 of the substrate 22 to be coated.
As substrate sizes become larger and larger, it will be appreciated that it would be desirable to provide a combustion deposition apparatus that can accommodate large-area depositions. Furthermore, it will be appreciated that the development of a scalable combustion deposition apparatus also would be desirable.
In certain example embodiments of this invention, there is provided a flame guard and exhaust system for use in a combustion deposition depositing system for forming a coating on a substrate via at least one flame of at least one burner. An external baffle is provided. An internal baffle is spaced apart from the external baffle, with the internal baffle to be closer than the external baffle to the burner. An exhaust duct is located over the external and internal baffle, with these baffles comprising a portion of the duct. First and second walls are to be respectively provided at opposing ends of the burner and joining the external baffle to the internal baffle so as to complete the exhaust duct. The external baffle is sized and positioned to (1) reduce an amount of air flow into a deposition area proximate to the at least one flame during operation of the combustion deposition depositing system and (2) serve as an external wall of the exhaust duct. The internal baffle is sized and positioned to (1) at least partially confine the deposition area to the area immediately under the burner face during operation of the combustion deposition depositing system and (2) provide an internal wall of the exhaust duct.
In certain example embodiments of this invention, a combustion deposition apparatus for use in combustion deposition depositing a coating on a substrate is provided. A burner is configured to create a flame in an area between the burner and the substrate, with the burner being sized such that it extends at least along the entire length of the substrate. A plurality of flame guard and exhaust systems are provided, with each said flame guard and exhaust system comprising: an external baffle; an internal baffle spaced apart from the external baffle, with the internal baffle being closer than the external baffle to the burner; an exhaust duct located over the external and internal baffle; and first and second walls to be respectively provided at opposing ends of the burner and joining the external baffle to the internal baffle so as to complete the exhaust duct. The external baffle is sized and positioned to (1) reduce an amount of air flow into a deposition area proximate to the at least one flame during operation of the combustion deposition depositing system and (2) serve as an external wall of the exhaust duct, and the internal baffle is sized and positioned to (1) at least partially confine the deposition area to the area immediately under the burner face during operation of the combustion deposition depositing system and (2) provide an internal wall of the exhaust duct. In operation, the flame causes precursor material to be combusted and heats the substrate to allow at least a portion of the combusted precursor material to form the coating, directly or indirectly, on the substrate. The flame guard and exhaust systems are provided on opposing sides of the first burner.
In certain example embodiments of this invention, methods of making these and/or other similar flame guard and exhaust systems also are provided.
In certain example embodiments of this invention, methods of making coated articles also are provided. These and/or other similar combustion deposition modules or systems also are provided. The substrate to be coated is provided to the module. The flame is used to (1) combust precursor material and (2) heat the substrate to allow at least a portion of the combusted precursor material to form the coating, directly or indirectly, on the substrate.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.